1. Field of the Invention
The present invention relates to sorting devices and more particularly, to sorting devices for wood chips according to their thickness, to be used in the production of paper pulp.
2. Prior Art
The great majority of devices used for sorting varying sizes for material chips generally utilize screens having an appropriate mesh that will permit chips smaller than certain dimensions in thickness, length and width to pass through the screen and be collected, while the rejected material passes over the screen for subsequent disposal.
Other prior apparatus for this purpose utilizes a plurality of equal diameter disks disposed in a plurality of rows, over which the material to be sorted is fed. The disks rotate in the same direction, which causes the material to progress along the sorting device. Such devices are intended primarily for a gross separation of chunky or elongated over sized chips from materials of a generally smaller size. The acceptable smaller sized chips pass between the disks relatively easily, while the over sized chips are held back by the disks and carried to the discharger. Long thin pieces which would be acceptable except for their length, because they are longer than the distance between disks, are transported crosswise to the direction of flow of the other chips to the discharge end of the apparatus.
When using such a device for gross sorting of wood chips, it is thus necessary that the material not be upset too much or the longer thin pieces will pass through the disks and contaminate the acceptable chips being collected. The disks are therefore of uniform diameter so that the chips will be horizontally transported along the device.
A further disadvantage associated with this latter type of prior art device is that when disks having a smooth outer peripheral edge are used, the material chips being sorted tend to slide over the disks and not be gripped thereby, and are therefore not as efficiently sorted as is desirable, which results in a substantial loss of otherwise usable material chips that remain with the rejected chips and are disposed of.
Another disadvantage associated with these prior art devices is that when some form of member having other than a circular disk shape is utilized, for example a star-shaped or other convoluted periphery, these members in adjacent rows are arranged to mesh with each other like gears while rotating at the same peripheral speeds in order to avoid upsetting the oversized chips and thereby interrupting their orderly travel along the tops of successive rows of disks, but this also results in carrying to the reject outlet a good number of chips which would be accepted if upset to present a different dimension to the spaces between adjacent disks.